Obtention of bioactive peptides from porcine liver and their application in meat products

Resumo

This doctoral thesis sought to contribute to the valorisation of porcine livers for obtaining peptides with antioxidant properties and incorporating them as natural antioxidants in pork patties, thus prolonging their shelf-life. Four enzymes, alcalase, bromelain, flavourzyme, and papain, with five different hydrolysis times 4, 6, 7, 8, and 10 h, and three molecular weight cut-off membranes, 30, 10, and 5 kDa, were selected to carry out the experiments of this research work, whose aims were: the study of the influence of the incubation time, type of enzyme and molecular size of permeates on the antimicrobial and antioxidant activities of the hydrolysates, the subsequent identification of antioxidant peptides, and finally, the study of the hydrolysates to prove their efficacy in delaying lipid oxidation in pork patties. The porcine livers were analysed for their nutritional contribution before experimenting with the hydrolysates. They showed a good nutritional profile, with low fats, and good amounts of oligoelements, essential amino acids, and proteins with a remarkable biological value. Then, the enzymatic hydrolyses were performed and the antimicrobial and antioxidant activities were assessed. From the results, it was concluded that the 3 factors studied significantly affected the bioactivities assessed. Regarding antimicrobial activity, none of the extracts showed inhibition against Gram-negative bacteria. Concerning Gram-positive bacteria, none of the extracts showed inhibition against Staphylococcus aureus. In general, only the growth of Brochothrix thermosphacta was inhibited by most of the extracts. Absolutely all the extracts showed antioxidant activities. The highest ABTS and ORAC activities were reached in hydrolysates obtained with alcalase. The extracts produced by bromelain and alcalase enzymes exhibited the highest FRAP values at 8 h of reactions and filtrated with 30 kDa. In contrast, the fractions filtrated by 30 kDa membrane of 4 h of hydrolysis with flavourzyme and 8 h with alcalase provided better results of DPPH. More than 70 differentially abundant peptides were identified with liquid chromatography coupled to a mass spectrometer using the SWATH-MS method. Some of them showed strong correlations with antioxidant activities. The addition of hydrolysates to the pork patties in a final concentration of 250 ppm did not affect their acceptability. However, solely aqueous extracts of porcine liver protein hydrolysates with bromelain successfully protected pork patties from lipid oxidation.